This project will examine the metabolic and physiological effects in vivo of naturally occurring genetic polymorphism in enzymes of glycolysis as detected by gel electrophoresis. An insect study system (genus Colias; Lepidoptera, Pieridae) will be used, in which an extensive polymorphic allele series at the phosphoglucose isomerase (PGI) locus is already under study in the field and at the in vitro level of enzyme kinetics. Initial work will confirm the organization of carbohydrate resource flow in adult Colias from dietary sugars, through processing in the fat body, to use in working muscle, gonads, etc. In this context, we will then study the effects in vivo, on relevant metabolic intermediate pool sizes and on flux changes through PGI and related reactions, of functional differences now known to exist in vitro among PGI allozyme genotypes. The physiological consequences of these effects for viability, flight activity, and reproductive effectiveness will be studied experimentally, to allow a clear understanding of the relation of the metabolic effects to natural selection which is already known to act on these variants in the field, and to clarify the mode of action of that selection. Available analytical models will be used and/or extended to connect among effects at different levels of organization. The overall results will advance understanding of allozyme polymorphisms, lead to progress in evolutionary genetics, and clarify the possible importance of allozyme variation for public health, in direct application to human genetics and indirectly via agricultural implications.